Poor eating behaviors, inadequate physical activity, and obesity are some of the most pressing public health problems facing youth and adults in the United States. Other weight-related problems, including unhealthy weight control practices and body dissatisfaction, are also of concern given their adverse health consequences. Information on trajectories of these problems over time, their transmission from one generation to the next, and risk and protective factors, is needed to guide public health interventions. The proposed longitudinal study, Project EAT-IV (Eating and Activity in Teens and Young Adults), builds on previous study waves in which data were collected over a 10-year period on a diverse population-based cohort throughout different stages of adolescence and into emerging young adulthood. Project EAT-IV will extend the follow-up of study participants to a 15-year period (1999-2014), from adolescence (ages 12-18) to young adulthood (ages 27-33). Data will be collected from approximately 2250 young adults representing diverse ethnic/racial and socioeconomic backgrounds, who participated in previous study waves. Additionally, for the first time: 1) data will be collected from participants' significant others when applicable (expected n 1100); 2) parenting practices will be assessed among participants who have children (expected n 1240); and 3) preadolescent (ages 9-11) and adolescent (ages 12-18) children of participants (expected n 340) will be recruited into the study and asked about their eating behaviors, physical activity, and weight-related problems. The main study aim is to longitudinally examine eating behaviors, activity patterns, and weight-related problems, along with individual and socio-environmental predictors of these outcomes, over the life course from adolescence to young adulthood and across generations. Key research questions include: 1. How do eating behaviors, physical activity patterns, and weight-related problems track over a 15-year period (1999-2014) in a diverse sample, beginning in adolescence and continuing through young adulthood? What individual-level and socio-environmental factors, throughout the life course from adolescence to young adulthood, predict these outcomes in young adults and influence their trajectories over time? 2. How do eating behaviors, physical activity patterns, and weight-related problems during adolescence, and relevant individual-level and socio-environmental factors in adolescence, predict young adults' parenting practices regarding eating, activity, and weight? What are the implications for their children, the next generation of youth? What factors in young adulthood modify the strength of these associations? Important and timely questions related to obesity and other weight-related problems across key developmental transitions throughout the life course will be addressed using innovative and longitudinal research strategies. Findings will be widely disseminated to guide the development of interventions, practices, and policies to improve the weight-related health of young adults and their children.